Casus belli
Casus belli is a Latin term meaning case of war. In the game, a country with a casus belli (commonly abbreviated to "CB") on another country is deemed to have a valid cause for war. When declaring war, the player is presented with a list of available CBs. They may pick a CB from the list or choose to declare war without a casus belli and accept the penalties of +30 aggressive expansion and −2 stability (halved with full Diplomatic ideas).
Each casus belli has a particular war goal associated with it, generally either controlling a particular province or winning a certain proportion of battles. Meeting the war goal will cause the war score of whichever side has achieved it to gradually rise (up to a max bonus of 25% at a rate of +0.4% per month).
The casus belli also determines what peace terms may be demanded at no or reduced diplomatic power cost; additionally, some CBs disallow some peace terms entirely. Extracting additional concessions beyond those of the original CB (unjustified demands) will cost
diplomatic power to be demanded.
Contents
List of casus belli[edit]
War goals[edit]
Each CB has an associated war goal. This describes what each side has to do to get ticking warscore, i.e. additional warscore over time from having accomplished the goal. Wargoals include:
- Take province / Defend province: Control a specific province. This may be a province chosen on declaring the war, or the capital. Each side gets ticking warscore as long as they control the target. Neither side gets ticking warscore if a third party (e.g. rebels) controls it.
- Show superiority: Have at least 10% warscore from battles. No side gets ticking warscore if neither has said warscore from battles
- Blockade ports: Amount and rate of ticking warscore scales by the proportion of blockading.
Triggered[edit]
A triggered casus belli appears when certain actions are performed (like insulting other countries), and can also be given by events and missions.
Triggered casus belli only last for a certain amount of time before they expire and are no longer valid.
Without Art of War, none of these CBs can be used by an overlord on a subject's behalf.
- The duration of the CBs is listed in months.
Casus belli | Wargoal | ![]() |
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Acquisition | Affected peace offers |
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Restoration of Union | Take capital | 240 | 100% | 100% | 100% | Given by missions or to senior personal union partner when a junior partner becomes independent, for a total war score cost of 60%.
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Defected Province | Take target province | 12 | 100% | 200% | 50% | When a province defects due to rebels |
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Canceled Loan | Superiority | 12 | 100% | 200% | 75% | Given to debtor when creditor defaults on a loan This used to be such an easy way to get a CB that AI always refuses loans since 1.4 (except Indulgent rulers). |
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Discovered Spy | Superiority | 12 | 100% | 200% | 75% | Given by two Japanese events involving ninja |
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Disloyal Vassal | Take capital | 120 | 100% | 200% | 50% | Given to overlord when a vassal breaks free |
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Imperial Liberation | Take target province | 60 | 100% | 200% | 75% | Given to the Emperor when he demands unlawful territory and the other country refuses |
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Diplomatic Insult | Superiority | 12 | 100% | 200% | 75% | By event and the "Send Insult" diplomatic action |
These options also affect the defender. |
Subjugation | Take capital | 120 | 100% | 200% | 50% | From vassalization missions and the Nobility estate when a diet is called |
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Obscure Documents | Take capital | 12 | 100% | 100% | 150% | By Russian "Time of Troubles" disaster event "False Dimitri Overthrown" |
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Religious Unity | Take capital | 24 | 100% | 200% | 75% | Given to the emperor when an HRE member refuses the emperor's demand for religious conformance |
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Border Friction | Take target province | 12 | 75% | 100% | 75% | Some events |
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Trade War | Superiority | 24 | 100% | 200% | 75% | By event Not to be confused with Trade Dispute or Trade Conflict. |
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Trade Conflict | Blockade ports | 24 | 100% | 100% | 100% | Via the "Justify Trade Conflict" covert action. Not available to Merchant Republics (they get their own version, see below). |
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Trade League Dispute | Blockade ports | 24 | 100% | 100% | 100% | Available to the leader of a trade league against countries they could otherwise justify a trade conflict against. |
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Annexation War | Take capital | 24 | 50% | 100% | 100% | Never This CB is broken and doesn't work properly, nor can it be obtained normally. It could have been a colonial conquest CB. |
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Government Form War | Take capital | 120 | 75% | 100% | 100% | By event (![]() ![]() |
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Forced ally to break alliance | Superiority | 120 | 100% | 200% | 75% | Given when a Great Power forces an ally to break their alliance with the country. |
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Crush the Peasantry | Take capital | 120 | 75% | 100% | 100% | Against HRE Peasant Republics (initially ![]() ![]()
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Peasant Revolt | Take capital | 120 | 75% | 100% | 100% | For HRE Peasant Republics (initially ![]() ![]()
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Holy War Feast of Pheasants |
Superiority | 60 | 75% | 125% | 100% | With ![]() ![]() ![]()
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Automatic[edit]
An automatic casus belli is given when certain conditions between the attacker and the defender are met. These last as long as the condition is still satisfied. The "advanced casus belli" are Imperialism and Nationalism and are gained at diplomatic technology 23.
Casus belli | Wargoal | Conditions | ![]() |
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Affected peace offers |
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Humiliate Rival | Take capital |
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100% | 125% | 100% |
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Conquest | Take target province |
With |
100% | 100% | 100% | |
Reconquest | Take target province |
With |
25% | 100% | 75% | |
Independence | Defend capital |
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attacker: 100% |
100% | 75% |
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defender: 50% |
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Colonial Independence | Defend capital |
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attacker: 100% |
100% | 75% |
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defender: 50% |
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Nationalism | Take target province |
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50% | 150% | 50% |
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Imperialism | Take capital | 75% | 100% | 75% | ||
Contain Hegemon | Take capital | 75% | 100% | 75% | ||
War Against the World | Take capital |
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75% | 100% | 75% | |
War for the Emperor Subject Daimyo attacking the Shogun |
Take capital |
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75% | 100% | 100% |
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War for the Emperor Independent Daimyo attacking the Shogun |
Take capital |
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75% | 100% | 100% |
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Annex Daimyo | Take capital |
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50% | 100% | 100% |
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Sengoku | Take capital |
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75% | 100% | 100% |
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Colonialism | Take target colony |
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25% | 100% | 50% |
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Liberation | Take capital |
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100% | 300% | 75% |
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Holy War | Superiority |
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75% | 125% | 100% |
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Defender of the Faith | Defend country |
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100% | 200% | 75% |
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Cleansing of Heresy | Superiority |
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75% | 200% | 100% |
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Excommunication War / Excommunicated Ruler | Superiority |
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50% | 125% | 100% |
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Trade Dispute | Superiority |
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100% | 200% | 75% |
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Trade League Dispute | Superiority |
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100% | 200% | 75% |
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Imperial Ban | Take target province |
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100% | 200% | 75% |
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Coalition | Superiority |
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10% | 100% | 75% |
The attacking war leader gets +30 war enthusiasm with this CB. |
Claim on Throne | Take capital |
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attacker: 100% |
200% | 140% |
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defender: 50% |
100% | 75% |
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Tribal Conquest | Superiority |
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75% | 100% | 100% |
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Tribal Feud | Take target province |
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75% | 100% | 100% |
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Revoke Electorate | Take capital |
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100% | 200% | 75% |
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Liberate Elector | Superiority |
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100% | 150% | 75% |
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Trade Protection | Blockade ports |
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100% | 100% | 100% |
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Crush the Revolution | Take capital |
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50% | 150% | 50% |
Both sides get an additional +50 war enthusiasm when at war with this CB. |
Spread the Revolution | Superiority |
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50% | 150% | 50% |
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Unify China | Superiority |
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50% | 150% | 50% | Attacker:
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Defender:
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Take Mandate of Heaven | Take capital |
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50% | 100% | 50% | Attacker:
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Defender:
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Humiliate | Take capital |
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0% | 0% | 0% |
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Religious League | Superiority |
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50% | 150% | 50% |
Both sides get an additional +50 war enthusiasm when at war with this CB. |
Support Rebels | Take capital |
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100% | 200% | 50% |
While at war with this CB, the targeted rebels' armies are friendly to attacker. |
Maya Confederation | Take target province |
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75% | 100% | 75% |
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Flower Wars | Take capital |
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100% | 200% | 50% |
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Force Migration | Take capital |
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100% | 100% | 100% |
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Force Tributary State | Take capital |
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50% | 200% | 50% | |
Expand Empire | Take capital |
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100% | 25% | 100% |
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Great Holy War | Superiority |
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75% | 200% | 75% |
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Conquest details[edit]
Having a claim allows the selection of the targeted province as a wargoal. The covert Fabricate Claims diplomatic action provides a claim on a single province (for details of which provinces can have claims fabricated on them, see Espionage § Covert actions). This is an immediate action that costs a certain number of points of spy network strength, starting at 20 and increasing by 5 spy network points per existing claim. In addition, many missions, events and unification national decisions give permanent or temporary claims, sometimes on a large region. There are also some events, such as Border Friction, that allow claims to be gained.
A temporary claim will expire in 25 years after a nation first gets the claim (permanent claims never expire). A claim can't expire during a war with the province's owner; permanent claims never expire, though they can still be given up in a peace deal. Regardless of CB used, claims provide −10% core creation cost, or −25% for a permanent claim.
Choosing a CB[edit]
Conquest is ordinarily the easiest CB to get by simply fabricating a claim, but also the least useful. Taking too many provinces can quickly result in a large coalition being formed against the country due to aggressive expansion (AE). It is still desirable to fabricate claims before fighting, in order to reduce coring cost and time, and the diplomatic point cost.
- Holy War and Cleansing of Heresy work on any heathen or heretic, which also removes diplomatic point cost for taking any province, and are both unlocked by the last Religious idea.
- If you have a special CB due to your government form or religion that allows you to take land, you'll usually be better off using it when possible, since it's tailored to your needs. Claims are still useful in these situations, but not strictly necessary. Daimyo, Maya reforming the religion, the Emperor of China, and steppe hordes all want to conquer land with less AE and maybe warscore cost, while Nahuatl trying to reform the religion want cheaper vassalization. The revolution target wants to Spread the Revolution (in fact it can hardly do much more), while their monarchist neighbours want to Crush the Revolution.
- Becoming revolutionary is a common world conquest strategy, because the bonuses of being the revolution target and the reduced warscore and diplomatic power cost of the revolutionary CB, in combination with
administrative efficiency from high absolutism, make it possible to conquer huge amounts of land very quickly.
- Becoming revolutionary is a common world conquest strategy, because the bonuses of being the revolution target and the reduced warscore and diplomatic power cost of the revolutionary CB, in combination with
- Note that a casus belli only reduces the cost of provinces that fulfill its criteria. For instance, Colonialism has 25% aggressive expansion and 50% warscore cost, but only for taking provinces that are overseas for both or from overseas colonial nations. Provinces on the same continent as the target's capital or directly connected to the capital will incur full costs (unless they're a colonial nation). When choosing such a CB, it will list the names of all the applying provinces, or show the number of these provinces if there are too many.
- Also note that the reduced warscore cost also affects options that are set on total province cost. So if a country's warscore cost is just over 100, the reduced cost for being wargoal might just make the country annexable/vassalizable.
If the goal of the war is not to seize territory or force-vassalize, then the choice of CB is less important, since extorting money or releasing nations doesn't cause AE. Conquest is fine to use in such a situation. If the country happens to be a rival and releasing vassals or countries is not desired, the special Humiliate Rival CB is ideally suited for this purpose. The drawback is that allies can't be called in on a promise of land with a CB that can't be used to fulfil that promise, so you will need favours.
Declaring war | Alliance • Casus belli • Claim • Peace • War exhaustion • Warfare |
Defense | Fort • Zone of control |
Land warfare | Army • Condottieri • Discipline • Drilling • Land units • Land warfare • Manpower • Militarisation • Mercenaries • Professionalism |
Naval warfare | Flagship • Naval blockade • Naval doctrine • Naval units • Naval warfare • Navy • Sailors |
Other | Force limit • Military leader • Military tradition |
Colonisation | Exploration • Colonisation • Colonial nation • Tariffs • Trade company |
Economy | Debase currency • Development • Economy • Privateering • Production • Raid coasts • Tax |
Trade | Trade • Trade company • Trade goods • Trade nodes |
Diplomacy | Diplomacy • Diplomatic feedback • Envoy • Espionage |
Other | Defender of the Faith • Great power • Hegemon • Prestige • Regions |
Political structures | Emperor of China • Holy Roman Empire • Papacy |
Relations | Personal union • Relations • Subject nation |
Concepts | Corruption • Governing capacity • Overextension • Power projection • Rebellion • Regions • Stability • States and territories |
Court | Advisors • Consort • Monarch power • National focus • Ruler • Ruler personalities |
Estates and Factions | Base estates • Cossacks estates • Dharma estates • Estates • Factions |
Events and Missions | Decisions • Disasters • Events • List of decisions • Missions |
Goverment | Absolutism • Culture • Government • Government rank • Modifiers • Policies |
Province mechanics | Autonomy • Buildings • Canal • Capital • Core • Province |
Religions | Christian denominations • Eastern denominations • Muslim denominations • Other denominations • Pagan denominations • Religion |
Specific governments | Native council • Parliament • Steppe hordes |
Ideas and Policies | Idea groups • National ideas • Policies |
Ages and Institutions | Ages • Institutions |
Innovativeness and Technology | Innovativeness • Technology |